Optical digital resolvers commonly comprise a resolver disc or slide with a multiplicity of digital tracks, and arrays of optical sources and detectors positioned adjacent the tracks. The sources and detectors are arranged so that each track is independently interrogated. For each track, an optical source provides an optical encoder input signal to a particular encoding site on the encoder member, and the encoding site modulates the optical signal to produce an encoder output signal. The encoder output signal from each detector is typically either high or low, depending upon when the bit being interrogated is a 1 or a 0. Resolvers typically operate with either a transmission or a reflection geometry, and the information is transmitted either continuously, or by time division multiplexing.
For many resolver applications, such as a hazardous or EMI prone environment, it is desirable that the resolver be electrically passive, i.e., it is desirable that the resolver does not require any external electrical power. Although such resolvers have been proposed in the past, such proposals have included a separate fiber for transmitting optical power to each track, and involved considerable optical complexity within the resolver itself. Wavelength division multiplexing has been demonstrated as a method for reducing the number of fibers between the resolver and the signal processing electronics, but this technique requires a complicated optical system within the resolver.